Mobile robots, such as mobile cleaning robots, may include a user interface on one or more surfaces thereof. The user interface may allow local user interaction or control of the mobile robot by direct input of operating instructions or commands via the user interface. Some user interfaces may include input elements in the form of physical and/or virtual buttons, with frequently used operating instructions or commands displayed thereon. For example, a user interface for a mobile cleaning robot may include “CLEAN” and “HOME” buttons that, when actuated, instruct the robot to perform a cleaning mission and return to its base or charging station, respectively. Such buttons may utilize mechanical and/or electrical detection to identify button actuation.
Electrical detection of user inputs at a user interface may include resistive and/or capacitive touch sensing. A typical capacitive sensor (also referred to herein as a capacitive touch pad, or touchpad) includes a conductor separated from the user by a thin insulator. The conductor is connected to a sensing device with a conductive trace. The touchpad can define a capacitor relative to other conductors in its vicinity. For example, the conductor of the touchpad may define a capacitor relative to the electrical ground plane of the sensing device, which may be used as a reference to measure the capacitance at the touch pad.
The capacitance of the touch pad/ground plane pair can change as the local environment (i.e., the volume of adjacent space through which the electric field lines 1003 flow between the touch pad 1001/ground plane pair 1002 changes, as shown in FIG. 10. Areas 1011 with denser electric field concentration (also referred to as field density) may be more sensitive to changes in the local environment, while areas 1013 with lower field density may be less sensitive.
The capacitance measured by the sensing device can be shifted by introducing a dielectric near the touchpad and/or by effectively adding external capacitance between the touch pad and the ground reference. For example, as a user's finger is inserted into the space through which electric field lines flow between the touchpad and the ground plane of the sensing device (e.g., above the touchpad), the capacitance (Cf) may increase due to the dielectric effect. In addition to such dielectric properties, a user may also be conductive and can act as an additional external capacitor. The effective capacitance of a user may be the inverse sum of all series capacitors in the path from the touchpad to the user to the robot, and may thus be smaller than the respective capacitances of the constituent capacitors, due to the serial connection.